Magnetism

Question 1

Permanent magnets

Answer 1

Permanent Magnets
- Always magnetic, always have poles
Induced Magnets
- Materials that are “magnetic” but do not have fixed poles
- These can be made into temporary magnets by ‘stroking’ them
with a permanent magnet
o These align the domains in the material all in the same
direction, creating a temporary magnet o Iron,Nickel,Cobalt

Question 2

Feild lines

Answer 2

Field Lines point from North to South
- Strength decreases with distance from the magnet
- Direction always points to south pole and away from north pole, at any point
- Use Plotting Compasses
o Small compasses which show the direction of the magneticfield at a certainpoint

Question 3

Earths core

Answer 3

The core is magnetic, and creates a large magnetic field around the Earth
- We know this because a freely suspended magnetic compass will align itself with the earth’s field lines and point North
- It doesn’t point to the Geographic North pole – it is over North Canada
- Also, the compass is effectively a suspended Bar Magnet, with its own north pole lining up with Earth’s ‘North pole’
o However this cannot be right,as like poles repel
o So Infact ,Earth’s magnetic pole above Canada is a
magnetic South Pole!

Question 4

Current

Answer 4

Current produces a magnetic field around the wire
- The direction is dictated by the “right hand grip rule”
- Plotting compasses on a piece of paper through which a
wire is pierced shows this

Question 5

Strength of field

Answer 5

Greater current, stronger magnetic field
- Greater distance from wire, weaker field

Question 6

Solenoid

Answer 6

Magnetic field shape is similar to a bar magnet
- It enhances the magnetic effect as coiling the wire causes the field to align and form a giant
single field, rather than lots of them all perpendicular to the direction of the current
- Having an iron core in the centre increases its strength as it is easier for magnetic field lines to
pass through than air
- Factors that affect the strength
o Size of current
o Length
o Cross sectional area
o Number of turns(coils)
o Using a soft iron core

Question 7

The motor effect

Answer 7

Two magnets will interact, feeling a magnetic force of attraction/repulsion
- So a magnet and a wire will also exert a force, as the two magnetic fields
(generated by the magnet and the current in the wire) will also interact
o Themagneticfieldaroundawireiscircular,butthemagneticfield
between two magnets is straight
o Whenthetwointeract,thewireispushedawayfromthefieldbetween
the poles (at right angles to the wire direction and the field direction)

Question 8

Flemings left hand rule

Answer 8

Thumb is force
Middle finger is field
Longer finger is current

Question 9

What properties have to be in place to experience the full force of the motor effect

Answer 9

The wire has to run pirpendicular no parralel otherwise it won’t run

Question 10

What is an electric motor

Answer 10

A current carry motor with side arms these forces act upon these arms
The negative side always goes down and the pot I’ve side always goes up
The split ring commander is a clever way of swapping the contacts every turn to keep the motor the spinning the right way
You can reverse the direction of the motor through reversing the polarity of the dc supply

Question 11

Properties of solenoids

Answer 11

You can increase the strength of the magnetic feild by wrapping a coil around a solenoid
This happens due to each loop of the wire lining up with each other
This results in lots of fuel lines point in the same direction that are very close to each other , the closer the feild lines are to each other the stronger the feild is